Solar collector

ABSTRACT

The invention provides a solar collector comprising a trough-like reflector for receiving solar rays and for concentrating the rays in a direction generally transverse to the length of the reflector between its ends. Concentrator means is provided for receiving the concentrated rays from the trough-like reflector and for concentrating the rays in one or more of a direction generally along said length and a direction generally transverse to said length.

CROSS-REFERENCE TO RELATED APPLICATION

This is a non-provisional U.S. application claiming priority from U.S.Provisional Patent Application No. 60/893,275 filed on Mar. 6, 2007, thedisclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to solar collectors, and in particular tosolar collectors which collect and concentrate solar rays.

BACKGROUND OF THE INVENTION

Solar collectors for collecting solar energy generally fall into one oftwo categories: concentrating and non-concentrating. Concentrating solarcollectors typically comprise a reflector for reflecting andconcentrating received solar radiation towards an absorber. The absorbermay include a conduit for carrying a heat transfer fluid for absorbingsolar thermal energy and/or an array of photovoltaic cells forconverting solar energy into electrical energy. The reflector is eitherin the form of a circular dish with the focal position above the centerof the dish, or a trough-like, parabolic reflector which produces a linefocus along the length of the reflector. In the latter case, theabsorber typically comprises a radiation absorbing tube positionedcentrally above the reflector and extending along its length.

Focussing or concentrating solar collectors typically require some typeof sun tracking mechanism and tracking control system to vary theorientation of the collector to maintain the focal position of the solarradiation of the absorber surface. Non-focusing solar collectorsgenerally comprise flat, solar absorbing panels which are fixed inposition and do not actively track the sun.

An example of a trough-like solar collector system is disclosed in WO2005/090873. The solar collector comprises a parabolic trough-likereflector having a longitudinal absorber positioned above the reflectorand mounted thereon by means of a central support upstanding from thereflector. The reflector includes spaced apart ribs fixed to theunderside of the reflector panel to help maintain the shape of thereflective surface. The absorber comprises a longitudinal plate having aradiation absorbing surface which may include an array of solar cellsmounted thereon. A conduit is positioned adjacent the back of the platefor transferring solar thermal energy into a heat transfer fluid.Transparent panels extend from each side of the absorber to opposedlongitudinal edges of the reflector to protect the reflective surfacefrom weathering and to provide additional structural rigidity.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided asolar collector comprising a trough-like reflector for receiving solarrays and for concentrating the rays in a direction generally transverseto the length of the reflector between its ends, and concentrator meansfor receiving the concentrated rays from the trough-like reflector andfor concentrating the rays in one or more of a direction generally alongsaid length and a direction generally transverse to said length.

According to another aspect of the present invention, there is providedan asymmetric solar concentrating trough based system, having means foractively tracking the sun on two axes; elevation (1) with individualtroughs and collectively with an array of troughs tracking on azimuth(2) with a primary (3) and secondary (4) mirror for concentrating thesun on two axes.

According to another aspect of the present invention, there is provideda symmetric solar concentrating trough based system, having means foractively tracking the sun on two axes; elevation (1) with individualtroughs and collectively with an array of troughs tracking on azimuth(2) with a primary (3) and secondary (4) mirror for concentrating thesun on two axes.

According to another aspect of the present invention, there is provideda two stage reflective solar concentration system where a first primaryoptical concentration reflector (3) is a two dimensional symmetric orasymmetric parabolic trough and second optical concentration stage (4)is a three dimensional modified paraboloid; both designed in combinationso as to provide a concentration ratio in the range from about 80 toabout 10,000 suns, or more.

According to another aspect of the present invention, there is provideda two stage concentration system with a third reflective or refractive(e.g. pyramidal frustum) optic stage (5) designed to accept theconcentrated sunlight rays (14) and mix them with multiple bounces so asto produce a substantially uniform illumination on the target surfacewithin about ±10% to ±30% maximum average illumination levels.

According to another aspect of the present invention, there is provideda solar concentrating receiver wherein heat is carried away from theconcentrated solar area (6) by heat transfer fluid (7) runninglongitudinally through the receiver in close proximity to the focal line(8) of the secondary 3D paraboloid (4).

According to another aspect of the present invention, there is provideda solar concentrator or receiver wherein a high efficiency multi-sunsolar cell (9) is placed at the solar focus area (6) to simultaneouslyproduce heat and electricity.

According to another aspect of the present invention, there is provideda solar concentrator receiver wherein a “cold” mirror (4) is used as thesecond stage mirror to remove solar radiation at least one of belowabout 400 nm and above about 700 nm, allowing substantially only thevisible light (10) only to pass through and where a translucent (fiber)optic light conductor (13) is placed at or near the solar focus area (6)allowing the transmission of visible light into buildings and/or areasrequiring light. The cold mirror prevents heat (infrared (IR) solarradiation) and plastic damaging (Ultraviolet (UV) Solar wave lengths)from entering the fiber optic light conductor (13), and acts in ananalogous way to a band pass filter in the electronics field.)

According to another aspect of the present invention, there is provideda solar concentrating receiver wherein one or more translucent lens(es)(11, 12) (e.g. planar or focusing translucent plate(s)) are placed inthe solar collection beam of light to remove the IR and/or UV solarradiation.

According to another aspect of the present invention, there is provideda solar concentrating receiver wherein either the cold mirror (4) ortranslucent lens (11, 12) are thermally interconnected to one or more UVand/or IR filters to efficiently and simultaneously capture the heat andfocus the light into the fiber optic light conductor (13).

According to another aspect of the present invention, there is provideda solar concentrator receiver wherein one or more thermal collectionpath(s) are thermally insulated with a thermal insulating material, e.g.mineral wool or similar high temperature, preferably, non-moistureabsorbing insulation.

According to another aspect of the present invention, there is provideda solar receiver wherein one or more of the fluid path extrusion (15)and the receiver cover (16) (if any) are continuous over the length ofthe primary mirror (3); and the secondary reflector or concentrator (4)and the secondary reflector cover (16) (if any) and the optical mixer(5) and optical mixer extrusion (17) are segmented in shorter sectionsso as to help keep precise alignment between the secondary reflector (4)and the mixer (5) during fluid path extrusion (15) heat up and cool downfrom about −40 to +100° C. for example, or any other operatingtemperature range.

In the above aspects of the invention, reference numbers in parenthesesrefer to features of the drawings, which are for illustrative purposesonly and in no way limiting of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments of the present invention will now be describedwith reference to the drawings, in which:

FIG. 1A shows a side view and part sectional view of a solar collectoraccording to an embodiment of the present invention;

FIG. 1B shows a front view of the solar collector of FIG. 1A;

FIG. 2A shows a perspective view of an array of solar collectorsaccording to an embodiment of the present invention;

FIG. 2B shows a side view of the solar collector array shown in FIG. 2A;

FIG. 2C shows a front view of the solar collector array shown in FIG.2A;

FIG. 2D shows a top view of the solar collector array shown in FIG. 2A;

FIG. 3 shows a perspective view of a solar collector according toanother embodiment of the present invention;

FIG. 4 shows a perspective, part sectional view of part of the solarcollector shown in FIG. 1;

FIG. 5 shows a perspective view of part of the solar collector shown inFIG. 4;

FIG. 6 shows part of the solar collector shown in FIG. 5;

FIG. 7 shows a perspective view of part of the solar collector shown inFIG. 4, and further including an optical waveguide;

FIG. 8 shows a graph of the spectrum of solar radiation versus energy;

FIG. 9 shows a perspective view of part of a solar collector accordingto an embodiment of the present invention;

FIG. 10 shows an example of a radiation mixer and graphs of irradianceas a function of area;

FIG. 11 shows an example of the geometry of an asymmetric solarcollector according to an embodiment of the present invention andexamples of the trajectories of solar rays; and

FIG. 12 shows a cross-sectional view through a mixer according to anembodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Referring to FIGS. 1A and 1B, a solar collector comprises a trough-likeprimary reflector 3 for receiving solar rays, a secondary reflector 4spaced from the primary reflector 3 for receiving solar rays reflectedfrom the primary reflector, and a receiver 20 for receiving solar raysreflected from the secondary reflector 4. In this embodiment, the solarcollector geometry is asymmetric, although in other embodiments, thegeometry may be symmetric.

The primary reflector is shaped to concentrate the reflected radiationtowards a focal line 21, which may be positioned in front of thesecondary reflector or mirror 4, although in other embodiments, thefocal line or position may be generally located behind the secondaryreflector. The surface of the secondary reflector is curved also toconcentrate the solar radiation in a first direction, e.g. x-directionshown by the arrow 22. The secondary mirror 4 is also curved in anorthogonal direction, along the z-direction (into the page of FIG. 1) toconcentrate light in the z-direction (i.e. longitudinal direction). Thereceiver 20 further includes an optical distributor 24 (e.g. mixer) forreceiving concentrated solar radiation from the secondary reflector 4and more uniformly distributing the solar radiation over a predeterminedarea. An alternative or additional function of this device is to assistin increasing the amount of received solar radiation from the secondaryreflector reaching a predetermined surface. The device may comprise areflective or refractive element or a combination of both. An embodimentof a reflective version of the device, shown in FIG. 5, comprises anelement having tapered side walls 25, 27, 29, 31, and having a first,receiving end 33 defining an aperture for receiving solar rays from thesecondary mirror 4, the side walls tapering inwardly towards an oppositeend 35 and defining an area 37. A solar converter may be positioned atthe opposed end 35 for converting solar radiation into electricalenergy. The size and shape of the light receiving surface of theconverter may substantially correspond to the size and shape of the area37 so that substantially all available concentrated radiation from thesecondary reflector and which enters the distribution device impinges onthe converter. The distribution device may have any suitable shape, sizeand geometry. In the present embodiment, the distribution device 5 isfrustopyramidal, having four flat tapered sides. In other embodiments,the distribution device may be conical, thereby forming a circular (orelliptical) area over which solar radiation is distributed, and whichmay be suitable, for example for circular solar cells. In otherembodiments, the distribution device may have any number of sides, e.g.three, five, six, seven, eight, etc.

In a refractive version of the distribution device, the device maycomprise a prism of solid translucent material, e.g. glass or othersuitable material and have any suitable shape as described above.

Referring to FIGS. 5, 6 and 7, the receiver 20 further comprises asubstrate 30 on which a number of distribution devices 5 may be mounted.FIGS. 5 to 7 show a solar cell 32 mounted on the substrate 30 having asolar radiation collecting area 6 which is registered with the lowerarea of the distribution device. In this embodiment, the substrate 30forms part of the wall of a fluid carrying conduit 40, which in thisembodiment has three fluid carrying channels, 41, 42, 43. Heat absorbedby the substrate 30 via an optional solar cell 32 is transferred throughthe substrate to fluid, e.g. liquid flowing through the conduits to asuitable point of use, such as space heating and/or to provide a sourceof hot water for example. In other embodiments, any number of fluidcarrying channels may be provided adjacent the substrate 30.

Referring to FIG. 7, the receiver includes a light pipe or opticalwaveguide 13 having a first end 45 which is positioned to receivesunlight from a distribution device 5 and has a second end 47 from whichthe light is emitted. The light transmitted by the waveguide 13 may, forexample, be used to illuminate interior spaces in buildings or otherspaces, where needed or desired. The optical waveguide may comprise anysuitable material, for example a polymeric or plastic material, glass orany other suitable material. The optical properties of the materialshould preferably be such as to minimize any light escaping from thesides of the optical waveguide, for example, the refractive index of thematerial may be such as to provide total or almost total internalreflection. The optical waveguide may comprise a single unitary memberor a plurality of individual waveguide members, e.g. a bundle of opticalwaveguides or fibres. The or each waveguide may have any suitablecross-sectional geometry, including rectangular or circular, and thelower end of the distribution device may be adapted to match the shapeof the end 45 of the optical waveguide.

A means may be provided for filtering one or more parts of the solarspectrum so that only selected wavelengths are admitted to the opticalwaveguide or other light receiver. Such means may include any one ormore of a coating on the primary and/or secondary reflectors 3, 4 whichselectively absorb certain wavelengths and reflect others, a lenspositioned between the primary and secondary reflectors 3, 4, a lenspositioned between the secondary reflector and the entrance aperture ofthe distribution device 5 and/or a coating on the reflective surfaces ofthe distribution device or a lens between the entrance aperture and thebottom portion of the distribution device.

Referring to FIGS. 4 and 7, the receiver includes a translucent member49 which is positioned above each distribution device 5 and may engagewith the upper peripheral edge defining the entrance aperture of thedistribution device to assist in holding each distribution device inplace, so that effectively, each distribution device is clamped betweenthe translucent plate 49 and substrate 30. The translucent plate or lensassists in protecting the receiver from the ingress of external elementssuch as atmospheric elements, e.g. moisture, dust and other particulatematter and also insects. The translucent plate 49 may also serve as afilter to filter out certain parts of the solar radiation spectrum.Portions of the spectrum which may be filtered using any one or more ofthe filtering means described above may include ultraviolet light and/orshorter wavelength radiation and/or infrared light and/or longerwavelength radiation.

In some embodiments, the receiver may include a combination of a fluidconduit and one or more solar cells, without any optical waveguides. Inanother embodiment, the receiver may comprise a combination of a conduitand one or more optical waveguides in the absence of any solar cells,and in another embodiment, the receiver may include a combination of aconduit, one or more solar cells and one or more optical waveguides. Inother embodiments, the receiver may include one or more solar cells inthe absence of any conduit or optical waveguide and in otherembodiments, the receiver may include one or more optical waveguides inthe absence of any conduit or solar cells.

Referring to FIG. 1B which shows a schematic front view of a solarcollector of FIG. 1A, the solar collector includes a plurality of armsor stantions 61 connected to the primary reflector structure along theedge thereof (or at any other suitable position) for supporting thereceiver 20. In this embodiment, the receiver comprises a continuoussubstrate 30 extending in the longitudinal (i.e. z) direction and whichis connected to each stantion either directly or indirectly via abracket 63 (shown in FIG. 4). The secondary reflector 4 is divided intoa plurality of discrete sections along the length of the solarcollector, and each secondary reflector section may be connected to thesubstrate 30 via suitable brackets 65. The sections 4 a, 4 b, 4 c may bemounted to provide a gap 67 between the ends of adjacent sections toallow the adjacent ends to move towards and away from each other withthermal expansion and contraction. In use, the substrate 20 may be at ahigher temperature than the secondary reflectors, and if made of asimilar material, the substrate will expand more in the z-direction thanthe secondary reflector. The difference in movement in the z-directionbetween the secondary reflector and the substrate on which eachdistribution device 5 is mounted may be reduced by dividing thesecondary reflector into discrete sections so that any differentialdisplacement occurs over a limited length of the secondary reflector.Maintenance of alignment between the secondary reflector 4 and eachdistribution device is also assisted by connecting the secondaryreflector to the substrate 20. Advantageously, these features allow eachsecondary reflector associated with a distribution device to remainsubstantially aligned in the z-direction so that most of the availableor substantially all light reflected and focussed by the secondaryreflector in the z-direction, as indicated by the broken ray lines 69,70, are directed into the distribution device entrance aperture. Thediscrete sections of the secondary reflector may have any desired orpredetermined length, and alignment between each secondary reflector andits corresponding distribution device may be improved as the length ofeach section decreases. In the illustrative embodiment of FIG. 1B, eachsection 4 a, 4 b, 4 c spans four distribution devices 5, although inother embodiments, a section may span any other number of distributiondevices, for example one, two, three, five, six or more. Referring toFIG. 4, the receiver includes upper, lower and rear housing panels orwalls 73, 75, 77 which enclose the receiver elements, including thesubstrate, distribution devices and conduit. Insulating material may beprovided within the housing in order to thermally insulate the fluidconduit, the substrate and any one or more other components of thereceiver.

In one embodiment, the housing panels and the fluid conduit may compriseextrusions which run continuously from one end to the other of a solarcollector. In one embodiment, and with reference to FIG. 4, the receivermay include a channel member 79 for seating one or more distributiondevices and which may be slidably coupled to the substrate 30 or capableof sliding relative thereto in the z-direction. The channel member maybe formed by extrusion. The channel member may also be divided intodiscrete sections along the length of the receiver and each section maybe associated with a corresponding secondary reflector section, forexample as shown in FIG. 1B. At least partially decoupling the mountingfor one or more distribution devices from the substrate 30 may alsoassist in preserving alignment between each secondary reflector and itsassociated distribution device with changes in temperature.

Referring to FIG. 4, the channel mounting has upper outwardly extendingflanges 81, 83 for mounting a translucent panel, e.g. filter or lensthereon. The channel section and flanges may all be formed as anintegral one piece extrusion.

Referring to FIGS. 2A to 2D, one or more solar collectors may be mountedfor rotation so that the longitudinal axis of the collector can bemaintained substantially perpendicular to the direction of the sun'srays as the earth rotates. Advantageously, this helps to ensure that theposition of focus of the sun's rays for each secondary reflector in thez-direction remains substantially fixed as the earth rotates to ensurethat the rays are reflected into each distribution device and are notoffset to one side or the other in the z-direction. This increases theamount of sunlight collected over a daily period. In addition, eachsolar collector can be mounted to rotate about a longitudinal axisthereof, for example rotational axis 1 shown in FIG. 1A so that thesolar collector can track the sun as its elevation changes over a dailyperiod.

FIGS. 2A to 2D show an array of solar collectors positioned one behindthe other and mounted together on a rotary support structure whichcollectively rotates the array about a vertical axis. The supportstructure includes a circular ring 201 with a framework positionedwithin the ring and upstanding therefrom for supporting each solarcollector. The ring is supported by a plurality of discrete supportmembers 203 spaced circumferentially around the support ring and whichmay include one or more bearing members and/or guide members forsupporting and guiding the rotary ring as it rotates. Rotation of thesupport structure may be driven by any suitable means such as a motorvia a cable attached at one or two different positions on the supportring or support structure and which is looped about a rotary drum orcapstan, driven by the motor.

FIG. 10 shows an embodiment of a distribution device (e.g. mixer) havinga frustopyramidal geometry and a graph showing the distribution ofirradiance over the area of its lower aperture.

FIG. 11 shows the geometry of the primary reflector 3, secondaryreflector 4 and distribution device 5 according to an embodiment of thepresent invention, with ray lines illustrating the direction of solarrays reflected by and impinging on each element. FIG. 12 shows a sidecross-sectional view through a distribution device illustrating multiplereflections in which each reflection results in forward travel of eachray towards the lower aperture 90 of the distribution device rather thanbackwards reflection towards the entrance aperture 88.

In embodiments of the solar collector, any one or more components maycomprise a suitable metallic material, for example aluminum or any othersuitable material. Where differential thermal contraction and expansionis an important consideration, components may comprise the same orsimilar material.

Other aspects and embodiments of the invention may comprise any one ormore features disclosed herein in combination with any one or morefeatures disclosed herein. In any aspect or embodiment of the invention,any one or more features may be omitted altogether or may be substitutedby an equivalent or variant thereof.

Numerous modifications to the embodiments disclosed herein will beapparent to those skilled in the art.

1. A solar collector comprising a trough-like reflector for receivingsolar rays and for concentrating the rays in a direction generallytransverse to the length of the reflector between its ends, andconcentrator means for receiving the concentrated rays from thetrough-like reflector and for concentrating the rays in one or more of adirection generally along said length and a direction generallytransverse to said length.
 2. A solar collector as claimed in claim 1,wherein said concentrator means comprises at least one of a refractiveelement and a reflective element.
 3. A solar collector as claimed inclaim 1, wherein said concentrator means comprises a plurality ofelements positioned relative to one another in a direction along thelength of the trough-like reflector.
 4. A solar collector as claimed inclaim 2, wherein one or more of said elements redirects rays in oppositedirections along said length to converge towards a predetermined area.5. A solar collector as claimed in claim 1, wherein said concentratormeans concentrates the received rays from the trough-like reflector in adirection transverse to said length.
 6. A solar collector as claimed inclaim 1, wherein said concentrator means concentrates solar raysreceived from the trough-like reflector towards a plurality of discreteareas spaced apart in a direction along the length of the trough-likereflector.
 7. A solar collector as claimed in claim 6, furthercomprising any one or more of a solar cell and an optical waveguidepositioned at one or more discrete areas.
 8. A solar collector asclaimed in claim 6, further comprising a ray distribution device forredistributing rays received from the concentrator means.
 9. A solarcollector as claimed in claim 8, wherein the distribution deviceincreases the uniformity of rays across at least one discrete said area.10. A solar collector as claimed in claim 6, wherein one or more of thedistribution devices comprises a reflective device having opposedreflective side walls for reflecting solar rays received from theconcentrator means.
 11. A solar collector as claimed in claim 10,wherein the distribution device is configured to prevent reflection bythe reflective walls back towards the concentrator means.
 12. A solarcollector as claimed in claim 6, wherein the distribution devicecomprises at least one wall which is angled in the ray direction towardsan opposed wall of the distribution device.
 13. A solar collector asclaimed in claim 1, further comprising one or more conduits for carryingfluid and which is positioned to receive thermal energy from solar raysemitted from the concentrator means.
 14. A solar collector as claimed inclaim 13, comprising first and second channels extending generally in adirection along the length of the trough-like reflector and means forcausing fluid to flow in a first direction along one of said conduitsand in the opposite direction along the other conduit.
 15. A solarcollector as claimed in claim 13, further comprising a plurality ofupstanding members spaced apart along the length of the trough-likereflector and being coupled or connected to the conduit or anothermember which extends substantially continuously between the ends of thesolar collector.
 16. A solar collector as claimed in claim 15, whereinsaid concentrator means is coupled to said conduit or said continuouslyextending member.
 17. A solar collector as claimed in claim 1, whereinsaid concentrator means comprises a plurality of discrete concentratorsdistributed in a direction along the length of the solar collector and,before thermal expansion, having a space therebetween to accommodatethermal expansion of each discrete concentrator in a direction along itslength.
 18. A solar collector as claimed in claim 17, wherein aplurality of discrete concentrators are coupled to a common memberextending in a direction along the length of the solar collector.
 19. Asolar collector as claimed in claim 1, further comprising a plurality ofdiscrete substrates positioned end to end in a direction along thelength of the solar collector and having a gap therebetween, a pluralityof discrete substrates being mounted to a common member extending alongthe length of the solar collector and optionally mounted on said commonmember in a manner which allows relative movement between the member andeach substrate in a direction along the length of the solar collector.20. A solar collector as claimed in claim 19, comprising at least one ofa solar cell and optical waveguide coupled to a discrete substrate. 21.A solar collector as claimed in claim 1, further comprising filter meansfor filtering out one or more portions of the solar electromagneticspectrum.
 22. A solar collector as claimed in claim 21, wherein saidfilter means comprises any one or more of a coating on the trough-likereflector, a coating on the concentrator means, a translucent memberbetween the trough-like reflector and the concentrator means, atranslucent member between the concentrator means and a means forreceiving solar rays from the concentrator means.
 23. A solar collectoras claimed in claim 21, wherein the filter means is adapted to filterout at least a portion of ultraviolet light and/or at least a portion ofinfrared light.
 24. A solar collector as claimed in claim 21, whereinsaid filter is adapted to transmit at least a portion of visibleradiation.
 25. A solar collector as claimed in claim 1, mounted on asystem capable of orienting the longitudinal axis of the solar collectorin a plurality of different directions.
 26. A solar collector as claimedin claim 1, wherein said solar collector is mounted on a system capableof rotating said collector about a longitudinal axis thereof.
 27. Asolar collector as claimed in claim 1, wherein a plurality of solarcollectors are mounted on a common structure, the common structureenabling the elevation of each solar collector to be controlledindividually or collectively such that each collector rotates about adifferent longitudinal axis and collectively the solar collectors rotateabout a common axis which is substantially vertical or upright.